Ion implantation is a technology of rapidly increasing importance in the fabrication of integrated circuits, particularly bipolar integrated circuits. In this bipolar technology, there is an increasing demand for (1) high dosage but relatively low time cycle implantation operations, and (2) ion implantation technology useful for introducing impurities through openings having at least one lateral dimension no greater than one mil. Since the implantation dosage is dependent on the combination of current and time, it follows that in order to achieve high dosage in relatively short time, the technology must move in the direction of high current ion implantation beams having currents greater than 0.5 ma. It has been found that when making such high current ion implantations of conductivity-determining impurities through electrically insulative layer openings having dimensions in the order of one mil as is required in the high density, large scale integrated circuits, there is a substantial tendency toward the impairment or destruction of portions of this electrically insulative layer resulting in potential short circuits which render the integrated circuit inoperative.
We believe that this impairment or destruction of the electrically insulative layer protecting the semiconductor integrated circuit is due to a charge buildup on this insulative layyer of the positive ions which make up the primary ion beam. This charge buildup is particularly pronounced in high current beams which have a high density of positive ions. In addition, when the openings through which the ions are to be implanted have small lateral dimensions in the order of one mil, secondary electrons which are normally produced by positive ions striking semiconductor substrate are minimized, and thus, there is an insufficient quantity of such secondary electrons available at the surface to neutralize the positive ion accumulation to prevent charge buildup.